The length is relevant because all of that dust, seen straight on, blocks a lot of light
Right, I see. I was thinking you meant that the huge length, seen lengthwise, would block a lot of light just because of the sheer length, but this makes more sense since lengthwise it wouldn't be that dense.
How about the other poster's brown dwarf idea? Could this be caused by a brown dwarf in orbit around the star? Those things can get really big. Effectively, it'd be a multi-star system. Or do brown dwarves emit enough light (probably in IR) to still be seen? And why is my stupid spell-checker telling me that "dwarves" is misspelled?